Automotive instrument panels and door panels are typically composites which are made of a rigid backing which supports a semi-rigid urethane foam with the semi-rigid urethane foam being covered with a skin compound. Such skin compounds are typically blends of polyvinyl chloride (PVC) with a nitrile rubber (NBR). The nitrile rubber is included in such blends as a permanent modifier for the PVC which provides it with a higher degree of flexibility.
The automotive industry is currently moving toward more aerodynamic body designs which typically include larger glass areas. Such design changes have significantly increased the heat and ultraviolet light aging requirements of automotive interiors. This has in turn significantly increased the demands put upon the polymers which are utilized as skins in automotive interior panels.
Heat and light stabilizers can be employed to improve the heat and ultraviolet light aging characteristics of conventional PVC/NBR blends which are utilized as skins for automotive interior panels. However, the degree to which the aging characteristics of such blends can be improved by the addition of additives is limited. In fact, there is a demand for performance characteristics in such applications which heretofore has not been realized by the utilization of heat and light stabilizers. For instance, it would be highly desirable for the skins used in automotive panels to resist discoloration and cracking under conditions of high heat and intense ultraviolet light throughout the life of the vehicle.
NBR/PVC blends offer an array of physical properties which make them useful as a skin composition for automotive panels. The NBR acts as a permanent flexibilizing monomer for the PVC. It also acts as a shrinkage control agent, and embossing aid, and improves grain retention. The NBR in such blends further provides vacuum forming gauge control and exhibits low fog characteristics. NBR is highly compatible with PVC and has the capability of being recycled. It is essential for any polymer which is substituted for NBR to display these essential characteristics.
U.S. Pat. No. 5,380,785 discloses a rubbery polymer which can be blended with PVC to make leathery compositions. These compositions are particularly useful in manufacturing skins for automotive interior paneling. Skin compositions which are made utilizing this rubbery polymer provide a higher level of resistance to heat and ultraviolet light than those made utilizing conventional NBR/PVC blends. The rubbery polymers of U.S. Pat. No. 5,380,785 also offer low fog characteristics, low odor, shrinkage control and grain retention. They also act as an embossing aid and as a permanent flexibilizing modifier. These rubbery polymers also have characteristics which make them useful in building gasket applications.
U.S. Pat. No. 5,380,785 also specifically discloses a rubbery polymer which can be blended with polyvinyl chloride to make leathery compositions having good heat and ultraviolet light resistance, said rubbery polymer being comprised of repeat units which are comprised of (a) butyl acrylate, or optionally a mixture of butyl acrylate and 2-ethylhexyl acrylate containing up to about 40 percent 2-ethylhexyl acrylate, (b) at least one member selected from the group consisting of methyl methacrylate, ethyl methacrylate, methyl acrylate and ethyl acrylate, (c) acrylonitrile, (d) styrene, (e) a half ester maleate soap and (f) a crosslinking agent. Polymers of this general type are sold by The Goodyear Tire & Rubber Company as Sunigum.RTM. rubber.
In Rapra Review Reports 73, Volume 7, No. 1, 1994, M W R Brown et al classified reactive processing methods into two groups:
(1) Methods where some form of polymerization or chain extension chemistry takes place during the making of an article, for example, reaction injection molding (RIM), reinforced reaction injection molding (RRIM), structural reaction injection molding (SRIM) and resin transfer molding (RTM).
(2) Methods where processing equipment, such as an extruder, is used for (a) the chemical modification of polymers, where the aim is to produce new or modified polymers or polymer blends or (b) the synthesis of polymers; i.e., materials which might be suitable for other different manufacturing methods such as injection molding.
The RIM, RRIM, SRIM and RTM methods are batch-molding process, while the REX (reactive extrusion) methods are continuous. The extruder can be regarded as some form of continuous chemical or polymerization reactor, where the reactants remain in the liquid or melt state inside the extruder; the final product only becoming solid after it has been cooled on emerging from the extruder.